Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/17/2023
Publication Date: N/A
Technical Abstract: Balancing dietary amino acid (AA) composition for lactating dairy cows is an important nutritional practice to optimize production, nitrogen use efficiency, and feed costs. Feeding rumen protected Met (RPM) is a common component of balancing for AA, but this practice may affect the concentration of other plasma AA (pAA). Therefore, the objective of this meta-analysis was to evaluate the changes in pAA when cows were provided supplemental Met. Literature studies were identified that fed cows a control diet and the control diet supplemented with Met as either RPM or through post-ruminal infusion. These studies also had to report multiple pAA (i.e. Met and >= 1 additional AA). This resulted in 40 publications feeding 60 control diets with 715 control cows and 78 Met treatments with 861 cows. Not all studies reported all AA with the number of treatment means reported for controls ranging from 8 for Hcy to 56 for several essential AA (EAA). Treatment responses were calculated as Met supplemented pAA concentration – control pAA. Since several pAA and responses to Met had skewed distributions, summary statistical analyses were conducted as weighted medians where the weighting term was the square root of the number of experimental units. Regression was also conducted where pAA was regressed against pMet weighted by the square root of the number of experimental units and including the random effects of study to statistically account for variance that can be attributed to study-related differences in management, genetics, etc. Significance was declared when P < 0.05 or trending toward significance when 0.10 > P >=0.05. Median pMet in control cows was 20 uM and pMet increased with Met supplementation, but the responses varied widely ranging from -2.1 to 62.3 uM. Regression analysis resulted in 11 AA associated with changes in pMet. Sulfur-containing AA Tau, Cys, and Hcy were increased and closely related (R2 = 0.881, 0.586, and 0.956, respectively) with increasing pMet whereas Tyr, Phe, His, Ile, Leu, Ser, and Val decreased with increasing pMet but did so less consistently (0.181 < R2 < 0.397). The largest reduction in pAA to increases in pMet was in Gly which declined 0.78 uM/uM pMet, although this relationship was somewhat inconsistent (R2 = 0.282). In conclusion, when formulating diets with supplemental RPM, the effects on the plasma concentration of other EAA and nonessential AA should also be considered.